If you are travelling from Central London to Heathrow airport (T1,2, or 3) then usually Heathrow Express train service seems the most obvious/quickest and convenient route.
This is often the case, trains leave Paddington every 15 minutes and takes about 15 minutes.... however the single journey fare is £15.50 per person !!! (geesh!)
However, most people don't realise there is a similar service (not advertised). It is called Heathrow Connect. Trains leave Paddington (like Heathrow Express) every 30 minutes and take about 25 minutes (about 10 minutes more than Heathrow Express) .... but the single journey fare is only £6.90 per person !!! That is a saving of an astonishing £8.60 !!
The train takes the exact same route, leaves from the same station, and arrives in the same station at Heathrow (T123).. the only difference is that it stops at a few local stations in West London (hence the extra 10 minutes journey time) ..
Most tourists / visitors don't realise there is an alternative. But there is... just 10 minutes extra journey time to save an amazing £8.60 each... well worth it don't you agree ?
The trains are modern, quiet, accessible, boast lots of luggage space, air conditioned.
Don't follow the crowd !